Adapt script to enable testing/developing with non-VPN OCI registries

[absoludity]

It'd be helpful to ensure that the script can be run with a github OCI registry rather than needing VPN access for publishing to projects-stg.registry.vmware.com .

This would enable other devs to run and improve the script, on their own GitHub repository and their own GitHub registry, without needing VPN.

[absoludity]

With this option, we could also avoid skipping the GitHub release when testing with the users' repo.